[clang] [clang][Modules] Reject export declarations in implementation partitions (PR #188698)

[Victor Chernyakin via cfe-commits]

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@@ -9931,9 +9914,10 @@ class Sema final : public SemaBase {
 
   /// Is the module scope we are an implementation unit?
   bool currentModuleIsImplementation() const {
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localspook wrote:

Looking at [the 3 callsites of this function](https://github.com/search?q=repo%3Allvm%2Fllvm-project+currentModuleIsImplementation&type=pullrequests), 2 of them really do want this new behavior: 
https://github.com/llvm/llvm-project/blob/e69c7312f31be57af5ef17ada7466b46f8519f2a/clang/lib/Sema/SemaModule.cpp#L701
https://github.com/llvm/llvm-project/blob/e69c7312f31be57af5ef17ada7466b46f8519f2a/clang/lib/Sema/SemaModule.cpp#L867
The last one AFAICT doesn't care:
https://github.com/llvm/llvm-project/blob/e69c7312f31be57af5ef17ada7466b46f8519f2a/clang/lib/Sema/SemaModule.cpp#L601
So maybe it's worth renaming the function to something like `currentModuleIsImplementationOrImplementationPartition`? (that's a really long name but I don't have a better one)

https://github.com/llvm/llvm-project/pull/188698